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<B><A HREF="PING.html">PING(8)</A></B> 		FreeBSD System Manager's Manual 	       <B><A HREF="PING.html">PING(8)</A></B>


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<H2>NAME</H2><PRE>
     <B>ping</B> - send ICMP ECHO_REQUEST packets to network hosts


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<H2>SYNOPSIS</H2><PRE>
     <B>ping</B> [<B>-QRadfnqrv</B>] [<B>-c</B> <I>count</I>] [<B>-i</B> <I>wait</I>] [<B>-l</B> <I>preload</I>] [<B>-p</B> <I>pattern</I>] [<B>-s</B>
	  <I>packetsize</I>] [<B>-S</B> <I>src</I><B>_</B><I>addr</I>] [<I>host</I> | [<B>-L</B>] [<B>-I</B> <I>interface</I>] [<B>-T</B> <I>ttl</I>]
	  <I>mcast-group</I>]


</PRE>
<H2>DESCRIPTION</H2><PRE>
     <B>Ping</B> uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit
     an ICMP ECHO_RESPONSE from a host or gateway.  ECHO_REQUEST datagrams
     (``pings'') have an IP and ICMP header, followed by a ``struct timeval''
     and then an arbitrary number of ``pad'' bytes used to fill out the pack-
     et.  The options are as follows:

     <B>-a</B>      Audible. Include a bell (ASCII 0x07) character in the output when
	     any packet is received. This option is ignored if other format
	     options are present.

     <B>-c</B> <I>count</I>
	     Stop after sending (and receiving) <I>count</I> ECHO_RESPONSE packets.
	     If this option is not specified, <B>ping</B> will operate until inter-
	     rupted.

     <B>-d</B>      Set the SO_DEBUG option on the socket being used.

     <B>-f</B>      Flood ping.  Outputs packets as fast as they come back or one
	     hundred times per second, whichever is more.  For every
	     ECHO_REQUEST sent a period ``.'' is printed, while for every
	     ECHO_REPLY received a backspace is printed.  This provides a
	     rapid display of how many packets are being dropped.  Only the
	     super-user may use this option.  <I>This</I> <I>can</I> <I>be</I> <I>very</I> <I>hard</I> <I>on</I> <I>a</I> <I>net-</I>
	     <I>work</I> <I>and</I> <I>should</I> <I>be</I> <I>used</I> <I>with</I> <I>caution.</I>

     <B>-i</B> <I>wait</I>
	     Wait <I>wait</I> seconds <I>between</I> <I>sending</I> <I>each</I> <I>packet</I>. The default is to
	     wait for one second between each packet.  The wait time may be
	     fractional, but only the super-user may specify values less then
	     1 second.	This option is incompatible with the <B>-f</B> option.

     <B>-I</B> <I>interface</I>
	     Source multicast packets with the given interface address.  This
	     flag only applies if the ping destination is a multicast address.

     <B>-l</B> <I>preload</I>
	     If <I>preload</I> is specified, <B>ping</B> sends that many packets as fast as
	     possible before falling into its normal mode of behavior.	Only
	     the super-user may use this option.

     <B>-L</B>      Suppress loopback of multicast packets.  This flag only applies
	     if the ping destination is a multicast address.

     <B>-n</B>      Numeric output only.  No attempt will be made to lookup symbolic
	     names for host addresses.

     <B>-p</B> <I>pattern</I>
	     You may specify up to 16 ``pad'' bytes to fill out the packet you
	     send.  This is useful for diagnosing data-dependent problems in a
	     network.  For example, ``-p ff'' will cause the sent packet to be
	     filled with all ones.

     <B>-Q</B>      Somewhat quiet output.  Don't display ICMP error messages that
	     are in response to our query messages.  Originally, the <B>-v</B> flag
	     was required to display such errors, but <B>-v</B> displays all ICMP er-
	     ror messages.  On a busy machine, this output can be overbearing.
	     Without the <B>-Q</B> flag, <B>ping</B> prints out any ICMP error messages
	     caused by its own ECHO_REQUEST messages.

     <B>-q</B>      Quiet output.  Nothing is displayed except the summary lines at
	     startup time and when finished.

     <B>-R</B>      Record route.  Includes the RECORD_ROUTE option in the
	     ECHO_REQUEST packet and displays the route buffer on returned
	     packets.  Note that the IP header is only large enough for nine
	     such routes; the <B><A HREF="traceroute.html">traceroute(8)</A></B> command is usually better at de-
	     termining the route packets take to a particular destination.  If
	     more routes come back than should, such as due to an illegal
	     spoofed packet, ping will print the route list and then truncate
	     it at the correct spot.  Many hosts ignore or discard the
	     RECORD_ROUTE option.

     <B>-r</B>      Bypass the normal routing tables and send directly to a host on
	     an attached network.  If the host is not on a directly-attached
	     network, an error is returned.  This option can be used to ping a
	     local host through an interface that has no route through it
	     (e.g., after the interface was dropped by <B><A HREF="routed.html">routed(8)</A></B>).

     <B>-s</B> <I>packetsize</I>
	     Specify the number of data bytes to be sent.  The default is 56,
	     which translates into 64 ICMP data bytes when combined with the 8
	     bytes of ICMP header data.  Only the super-user may use this op-
	     tion.

     <B>-S</B> <I>src</I><B>_</B><I>addr</I>
	     Use the following IP address as the source address in outgoing
	     packets.  On hosts with more than one IP address, this option can
	     be used to force the source address to be something other than
	     the IP address of the interface the probe packet is sent on.  If
	     the IP address is not one of this machine's interface addresses,
	     an error is returned and nothing is sent.

     <B>-T</B> <I>ttl</I>  Set the IP Time To Live for multicasted packets.  This flag only
	     applies if the ping destination is a multicast address.

     <B>-v</B>      Verbose output.  ICMP packets other than ECHO_RESPONSE that are
	     received are listed.

     When using <B>ping</B> for fault isolation, it should first be run on the local
     host, to verify that the local network interface is up and running.
     Then, hosts and gateways further and further away should be ``pinged''.
     Round-trip times and packet loss statistics are computed.	If duplicate
     packets are received, they are not included in the packet loss calcula-
     tion, although the round trip time of these packets is used in calculat-
     ing the round-trip time statistics.  When the specified number of packets
     have been sent (and received) or if the program is terminated with a
     SIGINT, a brief summary is displayed, showing the number of packets sent
     and received, and the minimum, maximum, mean, and standard deviation of
     the round-trip times.

     This program is intended for use in network testing, measurement and man-
     agement.  Because of the load it can impose on the network, it is unwise
     to use <B>ping</B> during normal operations or from automated scripts.


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<H2>ICMP PACKET DETAILS</H2><PRE>
     An IP header without options is 20 bytes.	An ICMP ECHO_REQUEST packet
     contains an additional 8 bytes worth of ICMP header followed by an arbi-
     trary amount of data.  When a <I>packetsize</I> is given, this indicated the
     size of this extra piece of data (the default is 56). Thus the amount of
     data received inside of an IP packet of type ICMP ECHO_REPLY will always
     be 8 bytes more than the requested data space (the ICMP header).

     If the data space is at least eight bytes large, <B>ping</B> uses the first
     eight bytes of this space to include a timestamp which it uses in the
     computation of round trip times.  If less than eight bytes of pad are
     specified, no round trip times are given.


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<H2>DUPLICATE AND DAMAGED PACKETS</H2><PRE>
     <B>Ping</B> will report duplicate and damaged packets.  Duplicate packets should
     never occur when pinging a unicast address, and seem to be caused by in-
     appropriate link-level retransmissions.  Duplicates may occur in many
     situations and are rarely (if ever) a good sign, although the presence of
     low levels of duplicates may not always be cause for alarm.  Duplicates
     are expected when pinging a broadcast or multicast address, since they
     are not really duplicates but replies from different hosts to the same
     request.

     Damaged packets are obviously serious cause for alarm and often indicate
     broken hardware somewhere in the <B>ping</B> packet's path (in the network or in
     the hosts).


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<H2>TRYING DIFFERENT DATA PATTERNS</H2><PRE>
     The (inter)network layer should never treat packets differently depending
     on the data contained in the data portion.  Unfortunately, data-dependent
     problems have been known to sneak into networks and remain undetected for
     long periods of time.  In many cases the particular pattern that will
     have problems is something that does not have sufficient ``transitions'',
     such as all ones or all zeros, or a pattern right at the edge, such as
     almost all zeros.	It is not necessarily enough to specify a data pattern
     of all zeros (for example) on the command line because the pattern that
     is of interest is at the data link level, and the relationship between
     what you type and what the controllers transmit can be complicated.

     This means that if you have a data-dependent problem you will probably
     have to do a lot of testing to find it.  If you are lucky, you may manage
     to find a file that either cannot be sent across your network or that
     takes much longer to transfer than other similar length files.  You can
     then examine this file for repeated patterns that you can test using the
     <B>-p</B> option of <B>ping</B>.


</PRE>
<H2>TTL DETAILS</H2><PRE>
     The TTL value of an IP packet represents the maximum number of IP routers
     that the packet can go through before being thrown away.  In current
     practice you can expect each router in the Internet to decrement the TTL
     field by exactly one.

     The TCP/IP specification states that the TTL field for TCP packets should
     be set to 60, but many systems use smaller values (4.3BSD uses 30, 4.2BSD
     used 15).

     The maximum possible value of this field is 255, and most UNIX systems
     set the TTL field of ICMP ECHO_REQUEST packets to 255.  This is why you
     will find you can ``ping'' some hosts, but not reach them with <B><A HREF="telnet.html">telnet(1)</A></B>
     or <B><A HREF="ftp.html">ftp(1)</A></B>.

     In normal operation <B>ping</B> prints the ttl value from the packet it re-
     ceives.  When a remote system receives a ping packet, it can do one of
     three things with the TTL field in its response:

     <B>o</B>	 Not change it; this is what BSD UNIX systems did before the
	 4.3BSD-Tahoe release.	In this case the TTL value in the received
	 packet will be 255 minus the number of routers in the round-trip
	 path.

     <B>o</B>	 Set it to 255; this is what current BSD UNIX systems do.  In this
	 case the TTL value in the received packet will be 255 minus the num-
	 ber of routers in the path <I>from</I> the remote system <I>to</I> the <B>ping</B><I>ing</I>
	 host.

     <B>o</B>	 Set it to some other value.  Some machines use the same value for
	 ICMP packets that they use for TCP packets, for example either 30 or
	 60.  Others may use completely wild values.


</PRE>
<H2>RETURN VALUES</H2><PRE>
     The <B>ping</B> command returns an exit status of zero if at least one response
     was heard from the specified <I>host</I>; a status of two if the transmission
     was successful but no responses were received; or another value (from
     &lt;<I>sysexits.h</I>&gt;) if an error occurred.


</PRE>
<H2>SEE ALSO</H2><PRE>
     <B><A HREF="netstat.html">netstat(1)</A></B>,  <B><A HREF="ifconfig.html">ifconfig(8)</A></B>,	<B><A HREF="routed.html">routed(8)</A></B>,  <B><A HREF="traceroute.html">traceroute(8)</A></B>


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<H2>HISTORY</H2><PRE>
     The <B>ping</B> command appeared in 4.3BSD.


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<H2>AUTHORS</H2><PRE>
     The original <B>ping</B> command was written by Mike Muuss while at the US Army
     Ballistics Research Laboratory.


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<H2>BUGS</H2><PRE>
     Many Hosts and Gateways ignore the RECORD_ROUTE option.

     The maximum IP header length is too small for options like RECORD_ROUTE
     to be completely useful.  There's not much that can be done about this,
     however.

     Flood pinging is not recommended in general, and flood pinging the broad-
     cast address should only be done under very controlled conditions.

     The <B>-v</B> option is not worth much on busy hosts.

4.3 Berkeley Distribution	 March 1, 1997				     4
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